1. Field of the Invention
The invention relates to a film, particularly for hygiene articles, having at least one layer that is produced by extrusion of an elastomer polymer composition and subsequently cross-linked. The elastomer polymer composition contains 40 to 90 parts by weight of a styrene block copolymer, 5 to 50 parts by weight of a plasticizer oil, and up to 10 parts by weight of a thermoplastic polymer. The layer formed by extrusion of the elastomer polymer composition is cross-linked by treatment with electron beams.
2. The Prior Art
An elastic film having the characteristics described is known from European Patent No. EP 1 228 144 B1. The thermoplastic polymers of the elastomer polymer composition consist of polymers that are compatible either with hard segments or with soft segments of the styrene block copolymer. The thermoplastic polymers promote three-dimensional cross-linking during the subsequent electron beam treatment. However, there is a need to further improve the degree of cross-linking and thereby also the physical properties of the elastic film. An elastic film that can absorb great forces and is characterized by little tendency to creep is desired.
An elastic film is known from International Application NO. WO 2004/005398 A1, which has a thermoplastic cover layer and an elastomer layer of a material that can be cross-linked with UV. In order to allow cross-linking by means of UV beams, the polymer composition of the elastomer layer must contain substances that act as photoinitiators, in a proportion of up to 60 wt.-%. During irradiation of the photoinitiators, free radicals are produced, which remove hydrogen, i.e. hydrogen ions, from the polymer chains of the elastomer layer. Different polymer chains can connect at the breakage points, thereby cross-linking the elastomer layer and improving the elastic and mechanical properties. However, during the decomposition of the photoinitiators under the UV irradiation, components having a low molecular weight, which can be physiologically harmful, can be produced and can migrate out of the film. Frequently, an undesirable odor also occurs, which is attributable to the photoinitiators, i.e. to their fragments. From the aspect of production technology, it is disadvantageous that when a photoinitiator is used, partial cross-linking of the polymer material made available for extrusion can already take place by means of natural UV radiation, thereby making extrusion significantly more difficult or even impossible. Furthermore, UV radiation sources have a high need for energy and are prone to failure during mass production.